1. Field of the Invention
The present invention relates to a machining condition adjusting device for electric discharge machining.
2. Description of the Related Art
A processing machine for industrial applications performs a machining process such that a desired final shape is obtained by applying a physical, electrical, or chemical action to a metal workpiece of, for example, tool steel, thereby gradually changing the shape of the workpiece. In general, the state of this machining process can be varied by changing control parameters called a machining condition.
The result of machining depends on the appropriateness of a selected machining condition. It is actually difficult, however, to instantaneously select an appropriate condition that meets required machining specifications. In electric discharge machining, for example, it is essential to select such a machining condition that the machining speed is high and an abnormal machining state can be avoided. The machining condition stated herein comprises a plurality of control parameters, each of which is selected from varying values.
Normally, an operator settles an optimum machining condition of an electric discharge machine by frequently repeating operations including monitoring machining states, such as voltage, current, short-circuiting, disconnection, machining speed, etc., during machining on the machine side, adjusting the used machining condition based on the result of the machining and a machining state during machining, and performing machining again under the adjusted machining condition.
A conventional determination process for a machining condition will be described with reference to the flowchart of FIG. 13.
First, information indicative of a target machining state (non-occurrence of disconnection/short-circuiting, target machining speed, etc.) is registered as required machining information (Step SA01). Then, a machining condition to be used for test machining is set (Step SA02). Here the machining condition is a combination of set values of machining voltage, machining speed, current, downtime, etc., during machining.
Then, test machining is started under the machining condition set in Step SA02 (Step SA03). Thereupon, the operator monitors and records the machining state during machining on the machine side until the end of the machining, or a machining state during machining output from an electric discharge controller is automatically recorded (Step SA04).
After the end of the test machining (Step SA05), whether machining is satisfactory or not is determined by the result of the machining and the machining state during machining recorded automatically or by the operator (Step SA06). If the machining is then determined to be unsatisfactory, the machining condition used for the test machining is adjusted (Step SA07), and the adjusted machining condition is regarded as the one to be used for the test machining. Thereupon, the program returns to Step SA02, in which the machining condition for the test machining is reset. Thereafter, the processing of Steps SA03, SA04, SA05, SA06, SA07 and SA02 is repeated so that the machining is determined to be satisfactory in Step SA06. A simple straight-line shape and a zigzag shape shown in FIG. 14 are used for the test machining.
However, the method of this type is inefficient, requiring much labor. On the other hand, Japanese Patent Application Laid-Open No. 2-153476 discloses adaptive control such that optimum machining is performed by determining the machining state during machining and varying the machining condition.
According to the method disclosed in Japanese Patent Application Laid-Open No. 2-153476, however, the machining condition is continually varied. If a single machine is used to repeat the same machining, therefore, an optimum machining condition for each machining cycle varies, so that the result of the machining also varies, inevitably.